Abrasive sheets and belts



Patented Mar. 20, 1951 St. Paul, Minn, assignors to Minnesota Mining & Manufacturing Company, St. Paul, Minn., a

corporation of Delaware No Drawin Substituted for abandoned application Serial No. 480,520, March 25, 1943. This application July 19, 1948; Serial No; 39,587

claims (01. 5i298) 1 r The present invention relates to new articles of manufacture and to a; method of producing the same, especially flexible composite articles-P The invention more particularly concerns abra-, sive articles of the coated abrasive type having two or more coatings or layers of material joined in adhering or contiguous relation, for example, such as an abrasive article comprising a porous absorbent or cloth backing coated or impregnated with a resinous or adhesive material of one type and having a dissimilar grit-bonding or binder coat which latter has a layer'or coating of abrasive grits embedded therein.

This application is acontinuation of our appli cation Serial No, 480,520; filed March 25, 1943, and now abandoned;

In certain aspects this invention may be regarded' as animprovement or further develop ment of the abrasive structure disclosed'in the copending application of Byron J. Cakes; Serial No. 293,192, filed September 2, 1939, which issued as Patent No. 2,357,350 dated September 5, 1944. Said copending application,- among other things, discloses an abrasive article having a cloth back ing which is treated o'r impregnated with a solu-'- tion of a vinyl resin and has a grit-bonding coat comprising a straight phenol-aldehyde resin, in which latter a layer or coating of abrasive grits are embedded, the abrasive article being sandsize'd or not, as necessary. Such article provides a major contribution over the prior art in that it provides an abrasive article of the coated abrasive type adapted to be used wet in such heavyabr'ading operations as the grinding or abrading of glass, marble,steel and the like.

We have now made further developments or improvements in this general type of article, both in terms of method ofproduction and in characteristics of the finished article. One of the problems in connectionwith the use of abrasive belts in the wet grinding or abrading of glass; steel and the like is that many of such belts;- as heretofore made, tended to cup when in use; that is, they tended to assume a curve shape, usually convex to the abrasive coated surface (but sometimes concave thereto), which meant that when the abrasive belt, moving at high speed, first contacted the workpiece; the outer portions of the belt (in' the case of the concave cupping)" would contact the workpiece first, thus providing two parallel grooves in the working surface, running parallel with thebelt. It willb'e" obvious that thi'sis undesirable in many abrading operations, where a uniform abrading and smoothing operation is desired. This is particularly true so-called area sanding, where the belt is brought into contact with the workpiece by a pressure pad or shoe against the back of the same; or where the workpiece is brought into Contact with the belt and the shoe or pressure pad is mounted in a stationary position.

7 In the making of abrasive belts of this general type in the past it has been the practice to treat or impregnate the' cloth or like backing with an organic solvent solution of a resin, especially of the thermoplastic type, e. g. polyvinyl acetals and butyrals ethyl cellulose and; organic polysulfide resins. Rather careful control was desired in impregnating backings according to such procedure, including rather careful control of the degree of plasticization of the resinous impregnating agent.

We have found that a general improvement canbe made in the desirable characteristics of the sheeted abrasive article or abrasive belt and at the same time a considerable reduction in cost can be effected by employing water emulsions or dispersions of various resinous materials, es: pecially of the type hereinafter illustrated, to treat and/or waterproof the cloth or other abrasive backings in the production of sheeted abrasive articles, especially of the type adapted to be used wet in abrading or polishing glass, marble; steel and the like. We have also found that the" impregnation is improved in certain respects bythe use of an aqueous dispersion, as distinguished from an organic solvent solution, where cloth or other porous hydrophilic types of backing materials are employed.

An object Of this invention is, accordingly, to improve the penetration of resinous or waterproofing material into a; cellulosic backingsheet; A further object is to eliminate or minimize the use of organic solvents in the saturation or impregnation of these backings A related object is toreduce the expense, health hazardand fire hazard which is related to the use of many volatile organic solvents. A further object is to increase the speed of the saturating operations. ll still further object is to provide coating or impregnating materials that have a more satisfactory range of; viscosity for ease in handling. A still further object is to produce an abrasive belt in which a cloth or cellulosic backing sheet hasbeenimproved-intensile strength and in heat resistance' as by the use of chemically crosslinked vinyl resins, as illustrated further hereinafter.

These and other objects and advantages will become apparent from the description taken as a whole.

The dispersions or emulsions which may be used in treating the cloth or other backing sheet are illustrated by the following examples:

pounds of the cold Water while stirring and was dissolved or dispersed therein by stirring and heating to 65 C., until a clear solution was obtained. Then the Duponol ME, ammonium per-sulfate and a part of the triethanolamine, dissolved in the remainder of the water, was added to the polyvinyl alcohol solution and the batch cooled to 52 C. Then a mixture of the vinyl acetate monomer, methyl methacrylate monomer, di ethyl fumarate monomer and the di-isoamyl ethylene difumarate (which latter is a divinyl compound of the non-conjugate type) was slowly added to the batch over a period of one hour, gradually allowing the temperature during that hour to rise from 52 C. to 71 G. Then the entire charge was held for one hour at 71 C., after which it was gradually brought up over a period of one hour to 84 C, The entire charge was then cooled to room temperature. Throughout the entire processing time the pH of the charge was maintained between 4 to 5 by slight additions of triethanolamine, as needed. The

our abrasive belts. A suitable method of impregnating the cloth or the like with the above composition (or with those described hereinafter) is to pass a web of the cloth through a bath of said milk-like dispersion or emulsion, whereby the cloth web is immersed therein, and then to pass the thus treated cloth'between squeeze rolls which eliminate the excess dispersion from the cloth. The web of impregnated cloth may then be dried, either wholly or down to a moisture content of about 15 to 25% of the water originally present in the dispersion. The web of cloth (either with 15 to 25% of the moisture of the dispersion remaining therein or with a comparable amount of water added) is then passed under tension through hot calender rolls, or the like, sufiicient tension being placed on the cloth so that there will be an extension in the length of the cloth of about 2 inches more or less per yard of length of the cloth web for a width of web of about 32 inches. This latter operation is important in helping to reduce stretching when the final finished belt is used wet in an abrading operation. The thus treated backing material may then be coated with a straight phenol-aldehyde grit-bonding coat, or with other suitable non-thermoplastic or heat convertible binder material and a layer of abrasive grits applied to said coating, preferably in oriented position. A sandsizing coat is also commonly applied after the binder coat has been given an initial set. Illustrative of a specific advantageous straight phenol-aldehyde type of grit-bonding material is that disclosed in the aforesaid copending Oakes appliction Serial No. 293,192. Certain heat-advancing alkyd resins, where desired, can be used in lieu of the phenolaldehyde resin in the binder and/or sandsizing coats. Also, urea-formaldehyde, melamine aldehydes and such non-thermoplastic materials as sodium silicate cements have some utility in making these types of articles, although, in general, the straight phenol-formaldehyde type of binder is generally superior.

The finished abrasive article, as just described,

' commonly used in the form of an abrasive belt,

resulting material was a milk-like smooth and stable emulsion or dispersion.

In the above example it will be noted that the vinyl acetate monomer, the methyl methacrylate monomer and the di amyl fumarate monomer are the reactants which become co-polymerized and chemically cross-linked by the di isoamyl ethylene difumarate. Only a relatively small amount of the chemical cross-linking agent is needed, as will be seen from the above formula. The Duponol ME is simply a convenient and commercially available material which may be used as an emulsifying and wetting agent. It is essentially a salt of a long chain solvent and is generally of the type of sodium lauryl sulfate. The polyvinyl acohol is present as protective colloid, and it and the Duponol ME (aided to some extent by the triethanolamine present) are emulsion stabilizers. The ammonium persulfate functions primarily as a catalyst, to effect the copolymerization and chemical cross-linking reactions. A small amount of octyl alcohol, for example, to the extent of 5% by weight of the total charge, or equivalent material, may be employed as a foam depressant.

The milk-like smooth stable dispersion, just described, is one of our contemplated materials for coating or impregnating an absorbent backing material, such as a cloth sheet, in making is a highly efficient article for abrading or polishing glass, marble, steel and the like, and is commonly used in high speed abrading operations. The impregnating or sizing coat, deposited from the aforesaid-milk-like dispersion, yields an impregnating coating which is insoluble in water and many other materials, including most of the organic solvents, and also lends to the abrasive belt the advantage that it is almost infusible and has a very much increased tensile strength over ordinary vinyl polymers or resins deposited from organic solvent solutions.

In efiecting impregnation or presizing of a cloth or other absorbent backing material, it is sometimes desirable to pass the Web of cloth or the like a plurality of times through the immersion bath, with intervening drying or partial drying, in order to get the desired weight of impregnation. Where the backing is a standard drills cloth, as commonly used in the coated abrasive industry, having a thickness of cloth illustrated by a weight of about 1 pound for an area of cloth of 2 /8 yards in length and 28 inches in width, an illustrative and desirable degree of impregnation or presize is illustrated by 28 to 30 grains of deposited impregnating solids per 24 square inches of such cloth.

Other examples of dispersions which may be employed in impregnatin or presizing the cloth 5... or like backing in making the abrasive articles of this invention are illustrated by the following:

The above ingredients maybe reacted in substantially the manner illustrated hereinabove in connection with Example I. It will be noted that the ingredients listed as (C) represent the ingredients which go into making up the final chemically cross-linked copolymer, and their counterparts in Example I will be readily recognized. It will be apparent that the di-isoamyl ethylene difumarate is the chemical crosslinking agent.

6 andfmethacrylate compounds, fumarates, styrenes, and the like, and a." may be hydrogen or and R may be an alkyl, aryl or ar-alkyl radical.

To illustrate better what is meant by chemical cross-linking reactions, where one mol of diallyl succinate, viz.

H,c=oH iH2 is used. as a cross-linking reactant for a large number of mols of: vinyl acetate monomer, viz: oH=oH o |3'oH'.

long chains of vinyl polymer or partial polymer are linked together to provide a chemical structure such as the following:

HzH

I H2 (OH COO) (CHaCOO),

(CH O 0) (CH & 0 0) (011343 0 O) Emample III Pounds A Water 2000 Polyvinyl alcohol 20 Duponol 14 Ammonium persulfate 10 Triethanolamine 5 C Vinyl acetate 750 Di-amyl fumarate 250 Di-isoamyl ethylene difumarate 2.5

the acetate radical occurrin in vinyl acetates or the radicals occurring in the various acrylates (011 O O) (011 O 0) Each of the vinyl chains may have a molecular size of a large number, e. g. to 400, of units of vinyl acetate monomer, with a total molecular weight of the cross-linked compound of several thousand, e. g. above 10,000, and often approximating or exceeding 30,000 or 40,000.

Various other chemically cross-linked materials, in addition to the one just illustrated and those shown in Examples I to III, may also be employed according to this invention. One additional example is the reaction and polymerization product of vinyl acetate monomer and allyl acrylate as a chemical cross-linking agent, although there are many other contemplated cross-linked resins.

By employing a dispersion of a cross-linked resin as illustrated in Examples I to III, we are able to obtain a coating which is continuous and is also insoluble in most solvents (including water and most organic solvents) and is almost infusible. This is a result which is unattainable by using resin solutions. Abrasive belts as above described can consequently be used at relatively high temperatures because of the increased heat resistance of the backing.

Hereinabove our invention has been illustrated by various details and specific examples. It will be understood that these are illustrative only and not limitative. All equivalents and novel variations Within the scope of this application are likewise contemplated. Chemically crosslinked polymers of controlled hardness and other characteristics, formulated as herein illustrated,

also have utility as binder and/or sand-sizing coats for coated abrasive articles for certain uses.

What we claim is:

1. A flexible abrasive article of the coated abrasive typ comprising a strong woven fibrous material; an impregnating or presizing coat for said fibrous material which consists of a filmforming elastic waterproof material comprising the polymerization product of a vinyl monomer reacted in the presence of a non-conjugate divinyl monomer as a chemical cross-linking agent; and a waterproof grit-bonding coat, and a layer of abrasive grits embedded in the latter.

2. The method of producing a coated abrasive articl which comprises treating a porous backing sheet with a dispersion produced by polymerizing a vinyl monomer in an aqueous dispersion in the presence of a divinyl chemical cross-linking agent; drying the thus treated backing so that the web of backing material has its streach substantially reduced; coating the backing with a grit binder coat of heat-advancing synthetic resin; electrostatically depositing a layer of abrasive grits in said grit-bonding coat and setting the resulting gritbonding coat.

3. An abrasive article of the coated abrasive type comprising a porous backing sheet; an impregnating or sizing coat for said backing sheet comprising a co-polymer of a vinyl monomer and a di-vinyl chemical cross-linking agent; an organic grit-bonding coat comprising a heat-advancing synthetic resin, joined to the impregnated backing sheet aforesaid; and a layer of abrasive grains partially embedded in and bonded by said grit-bonding coat.

4. An abrasive article of the coated abrasive type comprising a porous backing sheet; an im-.- pregnating coat for said backing sheet comprising a plasticized, chemically cross-linked vinyl acetate co-polymer produced by emulsion polymerization; an organic grit-bonding coat comprising a heat-advancing synthetic resin joined to said impregnated backing sheet; and a layer of abrasive grains partially imbedded in and bonded by said grit-bonding coat.

5. An abrasive article of the coated abrasive type comprising a porous backing sheet; an impregnating coat for said backing sheet comprising a plasticized vinyl copolymer including minor proportions of a divinyl cross-linking agent, produced by emulsion polymerization; an organic grit-bonding coat comprising a heat-advancing synthetic resin joined to said impregnated backing sheet; and a layer of abrasive grains partially imbedded in and bonded by said grit-bonding coat.

WILLIAM -J. MCNAMARA. JOSEPH H. KUGLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Oakes Sept. 5, 1944 

1. A FLEXIBLE ABRASIVE ARTICLE OF THE COATED ABRASIVE TYPE COMPRISING A STRONG WOVEN FIBROUS MATERIAL; AN IMPREGNATING OR PRESIZING COAT FOR SAID FIBROUS MATERIAL WHICH CONSISTS OF A FILMFORMING ELASTIC WATERPROOF MATERIAL COMPRISING THE POLYMERIZATION PRODUCT OF A VINYL MONOMER REACTED IN THE PRESENCE OF A NON-CONJUGATE DIVINYL MONOMER AS A CHEMICAL CROSS-LINKING AGENT; AND A WATERPROOF GRIT-BONDING COAT, AND A LAYER OF ABRASIVE GRITS EMBEDDED IN THE LATTER. 